Fuel cells are typically composed of a plurality of cell units with each comprising two electrodes (anode and cathode). These two electrodes are separated from each other by an electrolyte element and assembled with each other in series to form a fuel cell stack. Electrochemical reaction is implemented by supplying proper reactants to each electrode, i.e., supplying fuel to one electrode and oxidant to the other electrode, as a result, potential difference is formed between the electrodes and accordingly, electric energy is generated.
In order to supply reactants to each electrode, a particular interfacial element which is usually known as “bipolar plate” and disposed at two sides each individual cell is used. The bipolar plate is usually in the form of individual element disposed in the vicinity of anode or cathode support body. The bipolar plate is a key element for fuel cell pack. In the operating process of the fuel cell stack, the bipolar plates perform the following functions for the purpose of maintaining the optimal working state and service life of the fuel cell stack: (1) electrical conductor of cell, cathode and anode are formed at the two sides of the bipolar plate respectively, thus plenty of cell units are connected in series to form the fuel cell stack; (2) reaction gas (mass transfer) is supplied to the electrodes through channels; (3) managements for water and heat are coordinated so as to prevent medium cooling and leakage of reaction gas; and (4) structural strength support is offered to membrane electrode assembly (MEA).
To perform the functions above, the material of the bipolar plate requires high electrical conductivity, sufficient mechanical strength, excellent thermal conductivity, low air permeability and corrosion resistance, and is capable of being chemically stable in a working environment of cell for a quite long time. Furthermore, in view of the requirements on design as well as processing and manufacturing easiness, the material of the bipolar plate should also have the features of light weight, small size, low cost, and even recyclability, etc.
The material adopted must be electrochemical corrosion-resistant and superior in structural strength and stability owing to the electrochemical reaction working environment of fuel cell. Hence, factors in all respects must be taken into full consideration when a high-performance bipolar plate for cell is designed. Typically, the materials of the bipolar plate for cell include: carbon plate, metal plate and the like. Traditionally, the use of carbon plate as polar plate for cell is attributed to its good electrical conductivity, heat transfer property and corrosion resistance. And the reason for using metal plate lies in its excellent electrical conductivity, structural strength and formability and in the fact that it is still a good material of electrode plate even after anti-corrosion surface treatment.
In addition, considering that the manufacturing cost of polar plate for cell is high, to lower the cost of fuel cell, one of the attempting directions in fuel cell's design is to seek for the design and manufacturing method for optimizing the bipolar plate for cell.